I use an elcheapo digital camera, and two different Visioneer scanners. I use Paint Shop Pro to load any images into the machine. When I connect any of these devices, I must first open PSP, then click File > Import > Twain > then, select source/acquire...I usually have to select source first because (maybe) one of the scanners was last used.
Maybe this is not your problem...needing to select the source, but could be?...